In a large bowl, whisk together the egg, milk, canola oil, and vanilla. Mix the dry ingredients into the wet ingredients and spread into pan (you might want to grease your spatula). Set aside.

In another large bowl, whisk together remaining 2 1/2 cups flour, brown sugar, and cinnamon (and allspice, if using). Pour melted butter over flour mixture, and stir with a rubber spatula until large crumbs form. Spread evenly over batter in pan. Sprinkle with powdered sugar, if desired.

Bake at 325F for 25-30 minutes, rotating once, until a tester comes out clean.